1. Field of the Invention
The present disclosure relates to pressure measurement devices, and more particularly to capacitive pressure sensors for high temperature environments.
2. Description of Related Art
Conventional sapphire-based high temperature capacitive pressure sensors generally include a thin diaphragm wafer coupled to a thick substrate wafer with a uniform depth recess. The wafers typically include separate electrodes, one electrode being formed on the diaphragm wafer surface and the other being formed in the substrate recess. The wafers are bonded together such that the substrate recess forms a main recess gap separating the electrodes. Through vias typically extend through the substrate wafer and the substrate wafer recess, physically and electrically connecting with the electrodes. This allows for measuring the capacitance between the electrodes. Capacitance is a function of the main recess gap height. The main recess gap height changes in response to external pressure, changing capacitance as a function of external pressure and allowing for measurement of external pressure. The main recess gap depth is generally determined by pressure sensor's mechanical and electrical designing characteristics such as external pressure range, read-out capacitance, sensitivity and reliability.
A via recess provides housing for all electrical connection between the through vias and the electrodes. In applications when a hermetic pressure chamber is required, via sealing, such as with a conductive paste or with conductive thin films, is typically applied to seal the through wafer vias such that the internal pressure chamber formed by the substrate recess is separated from the environment external to the sensor. For both conductive paste via sealing and conductive thin film via sealing, a small via recess gap is desired to minimize the conductive paste flowing into the pressure chamber and to minimize the total amount of the conductive thin film deposition.
In most of the conventional capacitive sensors, the via recess is defined at the same time when defining a substrate recess or a diaphragm recess. Also, in some of the conventional capacitive sensors, via recesses are defined in both the substrate and the diaphragm wafers. In both cases, the total via recess depth is dependent on the pressure chamber depth design, in which case, the via recess depth may not be optimized for the via sealing when a hermetic pressure chamber is required. This present disclosure provides one solution to address these issues.